A two-dimensional map display device which is represented by a car navigation device displays a bitmapped image called a symbol as each indication icon (e.g., an icon showing a convenience store, a bank, a gas station, or the like). While these symbols are usually drawn by using a two-dimensional drawing core, a method of drawing a two-dimensional symbol using a three-dimensional drawing core has been developed following recent developments in such a three-dimensional drawing core.
Symbol drawing using a three-dimensional drawing core uses a 3D graphics technology. Therefore, when aiming at an improvement in the speed of drawing, a high-speed drawing method for use in a typical 3D graphics technology is effective. There is a method called texture atlas as one of speeding up techniques. In three-dimensional drawing, a two-dimensional image called a texture is mapped onto a polyhedron called a polygon which consists of a plurality of vertices, so that various expressions, such as buildings for use in a racing game and characters for use in an action game, can be achieved.
However, when mapping a different texture onto each polygon, switching the texture to be used between textures is required, but the process of switching between textures is generally carried out at a low speed. Therefore, a map symbol drawing device that reduces the number of times that a texture switching process is carried out at a time of drawing by incorporating a plurality of textures into a single large texture (texture atlas) in advance in order to provide an improvement in the speed of drawing is disclosed by the following patent reference 1. More specifically, the map symbol drawing device disclosed by the patent reference 1 generates a texture atlas for each part in a three-dimensional model, such as a character, thereby preventing the process of switching between textures from being carried out at the time of drawing each part.